Problem with tummy fat

Asked for Female, 25 Years

My height 5.2 inc, weight 50.5 kg, But the problem is my upper body looks very thin but had more fat in tummy(buttocks,thighs). I feel very insecure about this. I wanted to get rid of this fat an gain muscle in my upper body. what would be the best way? first i need to get rid of unwanted fat and then gaining muscle or now itself try for muscle gain.